1. Field of the Invention
The present invention relates to a pattern forming method for forming fine-line patterns, and an ink composition, and more particularly to a forming method suitable forming a cathode-ray tube anode, and graphite ink and phosphor ink used in cathode-ray tube or plasma display.
2. Description of the Prior Art
In the conventional cathode-ray tube anode process of color television manufacture, the surface of the glass substrate composing the phosphor plane was properly treated, and patterned, exposed and developed in a polyvinyl alcohol-ammonium dichromate photosensitive fluid, then a black substance such as graphite was rolled on the developed pattern, and the black matrix was formed by peeling and processing. The phosphor patterning was a complicated process to form each layer of R, G, B after three repeated sequences of spreading, drying, exposing, developing and drying of the slurry having the phosphor pigment dispersed in the polyvinyl alcohol-ammonium dichromate photosensitive fluid. In addition, before forming the metal-backed layer, an organic film layer was formed on the phosphor film as an interlayer, and the metal-backed layer was subjected to vacuum deposition. Afterwards, the glass substrate was fired at about 450.degree. C. and formed.
The above cathode-ray tube anode forming process is very long and complicated in procedure, and requires a huge volume of water owing to wet process, and discharges much waste water containing public nuisance materials. Besides, regarding the precision of the pattern formed by wet process, since exposure and development were repeated, edge linearity, lack of hiding, lack and other defects occurred, and it was difficult to obtain patterns of high quality. Still worse, it required an enormous plant investment because of vacuum deposition of the metal-backed layer.
Recently, meanwhile, the development of liquid crystal color panel is intensive. The color filter used in this liquid crystal color panel is formed mostly by the technology of photolithography, and the process was very long, including the steps of color film forming, photoresist film forming, exposing and developing, and the yield was very low and the product was hence very expensive.
To eliminate such defects, various printing methods, that is, dry processes have been proposed. For example, as the ink composition for forming cathode-ray tube anode by screen printing or offset printing, a composition containing acrylic resin was disclosed in the Japanese Patent Publication No. 55-41671, but it was not commercially established yet. The reason is, among others, that a relatively large film thickness is required for the black matrix and the phosphor pattern while very fine-line patterns are needed. To add to the film thickness, the density of the ink layer must be raised, which forces to raise the ratio of the pigment component in the ink higher than in the ordinary composition. As a result, however, the printability is extremely impaired, and it is difficult to satisfy the desired pattern precision. Or when the pigment content in the ink is lowered in consideration of printability, the luminance is lowered and other adverse effects are brought about. In other words, in the screen printing intended to print very fine-line patterns of thick film on a glass substrate, the precision is not sufficient, and satisfactory printing is not possible even by the gravure offset printing. Or in the graphite paste for black color printing using only acrylic resin, the adhesion strength to the glass surface was poor, the exfoliation of black matrix and phosphor layer was noted.